Magnetic device



ocr, s, 192s. E. L. NRTN v V1,733;5254

MAGNETIC IDEYICE..

Filed oct. 30.4 1926 Patented Oct. 29, 1929 UNITED., STATES hPA'rlazN'r oFFlcE EDWARD L. NORTON, OF NEW YORK, Y., ASSIGNOR TO BELL-TELE1HONE LABORA- TORIES, INCORPORATED, OF NEW YORK, N Y., A CORPORATION 0F NEW YORKV y MAGNETIC DEvrcE ppncation med oetober so, 1926. serm No. 145,114.

- This'invention relates to magnetic devices and more particularly to an arrangement for controlling the magnitude of response of signal actuated devices such as telephone re- .5 ceivers.

In accordance with this invention there is provided a 'telephone receiver in which acoustic shock is eliminated by theuse of inserts of magnet-ic material in the flux circuit which saturate abruptly and from which the major portion of the direct fiux from the permanent magnet is at all times excluded. Since that variety of permalloy composed of 7 81/2% nickel and 211/2% iron is a material l; in which saturation sets in abruptly, it is preferred yto use this material forl the iux limiting elements, however,other varieties of permalloy may be used. Permalloy may be defined as an alloy containingnickel tothe extentof 30% or more, balance chiefly iron,

Y and having the characteristic property 'of high initial permeability. f

By Yexcluding the maj or portion of the iux of the permanent magnet from the flux limiting elements itis possible toV make these elements small and to avoid decrease in the cuto point which would otherwise occur as the permanent magnet deteriorates in strength.

Moreover the diiferencesin strength of vari- :39 ous magnets as ordinarily employed 'in the manufacture of receivers may be neglected in the design of these flux limiting elements.

A device constructed on this principle Vmay take the form of an electromagnetic structure ofthe general type disclosed in U.- S. Patent of H. C. Harrison, No.4 1,709,571,y granted April 16, 1929, modified in accordance with this invention by splitting each pole piece transversely and inserting a section of perm- 40 alloy between the split parts. This embodiment of the invention is described in detail in the following. specification and Villustrated in the drawings. v

Fig. 1 is a side elevationalview, partly in ,4Q section, `of a telephone receiver 4containing electromagneticelements constructed in accordance with this invention; Fig. 2 is a rear elevational view ofthe electromagnetic elements shown in Fig. 1; Fig. 3 is a cross section taken online '3-3 of Fig. 2'; vwhile Fig. 4' showsthe armaturel of the electromagnetic device and its suspension means.

Referring now to the drawing, the electromagnetic device comprises a permanent steady-field U-shaped magnet 1, on the ends of which are mounted'pole pieces 2 and 3, which, however, are separated from direct connection with these ends by means of'permalloy inserts 4 and 5. These inserts are provided to give uniform magnetic action from magnets varying in strength, as described and shown in the above mentioned patent. They constantly limit the flux by Virt-ue of being constantly saturated.

It will be noted that the pole pieces 2 and 3 are each split in twoparts and connected together respectively by pins 6 and `7 of reduced cross sections. These pins are preferably made of 'permalloy or other suitable material. `Between the pole pieces 2 and A3v is mounted the armature 10 having wedged shaped extensions 11 in position lto be acted upon by the separate parts of the pole pieces 2 and 3. This arrangement is clearly shown in -v Fig. 3. 1 The armature is secured to a mounting member12 extended at right angle to the extensions 11. This member is provided with a groove registering with a knifeedgedwportion extending from the mounting block 13, which in turn is attached by means off-screws to the upper surface of one part of the pole piece 3. The'armature is held in place by a spring 14 secured at one end to the mounting block 13 and'extending beyond and over ythe member 12 so as to press it against the knifeedge on the 'block 13. The spring 14 is also kused to balance the armature against the pullof iield.r The angular extension 15 on lthe member 12 is employed to transmit motions of the armature to the diaphragm 18 through the connecting rod 16. The energizing coils 19 for the armature are mounted on either side of the member 12 around the ex tensions 11 of the armature 10 so that the armature is free to move in and be influenced by electromagnetic fields produced by the coils When energized by fluctuating currents. A housing 20 is provided for enclosing this magnetic structure and the ear piece 21 is arranged therein as shown for the purpose of utilizing the electromagnetic element as a receiver.

Referring now to the functions of the device it is evident that when the coils 19 are energized by a fluctuating current, such as, for example, the talking current in ordinary telephone circuits, the varying magnetic iux component produced by these coils initially passes primarily through the main portions 20 of the armature, the extensions 11, pole pieces 2 and 3 and the permalloy inserts 6 and 7, along the paths indicated by the arrow points in Fig. 3. This flux tends to displace the armature from its balanced position between 5 the pole pieces in accordance with the iluctua-` tions of the energizing current. In View of the restricted paths for the llux through the permalloy inserts 6 and 7 and due to the fact that these inserts reach the saturation point on a rat-her small increase in the magnetic iiux beyond the maximum operating value. the armature will not be noticeably displaced beyond the maximum operating limit `by ab normal currents, such as ordinarily produce acoustic shock. The displacement effects up to the saturation point are, as in the usual construction, substantially proportionalto the amplitudes of the current variations, and the armature, therefore, under such circum- 40 stances acts to reproduce corresponding described it is im acoustic effects through the diaphragm as in any ordinary receiving unit having a similar structure.

In the embodiment of the invention herein racticable to exclude all of the flux derived rom the permanent magnet from the iiux limiting elements except when the armature is in a balanced condition; that is, midway between the poles, When the armature moves from this position the system isunbalanced with respect to the iux from the magnet. Some of this flux then passes through the armature lengthwise and some of it through the permalloy inserts.

But this unbalanced variable component may 6o elements may, therefore,

be made small compared with the total flux and will therefore vary but little with relatively large variations in the strength of the permanent magnet. The vcurrent limiting as explained above, be designed to have a cut-oif point just above the operating range without dangerof moving the cut-off point Within the operating range or removingit-unnecessarily far from 'c5 the voperating range by changes in the strength of the magnet or the substitution of a different magnet.

It is evident that the invention is not limited to any particular construction but may be applied in various Ways to different types of apparatus. For example, the flux limiting inserts or sections may be located either in the armature itself or in the magnetizing system therefor provided they are not placed so as to be traversed by the steady fiuX component.

What is vclaimed is:

1. A magnetic device comprising means for producing magnetic flux having. a steady component and a variable component, and means traversed by the variable' fiuX component but not by the steady iiux component for preventing abnormal flux densities in the variable flux path.

2. A telephone receiver comprising means for producing magnetic flux comprising a steady component and a variable component, and means traversed bythe variable flux component but not by the steady flux component for limiting the fiux in the Variable flux path.

8. An electromagnetic device comprising a field magnet, an armature, a coil for variably energizing said device, and means in the path traversed by the variable flux component for limiting the maximum flux through said path and so arranged as not to be traversed by theI steady flux component.

. 4. An electromagnetic device comprising a field magnet, pole pieces for said magnet, an armature between said pole pieces, a wind ing for producing variable flux through said armature and said pole pieces, and means in said pole pieces for limiting thev maximum value of the variable flux component.

5. An electromagnetic device comprising a field magnet, an armature,a coil for variably energizing said device, and a permalloy section traversed by the variable flux but not by the steady flux for limiting the maximum iux through the variable iiux path.

6. n electromagnetic device comprising a permanent magnet, a coil for variably energizing said device, and means comprising pennalloy. sections in the path traversed by the variable fiux component for limiting the maximum luxthrough said path, said permalloy sections being so `placed as not to be traversed by the steady flux component.

7. lAn electromagnetic device comprising a eld magnet, an armature, means for variably energizingV said device, and means for limiting the maximum response of the armature to variable energizations to substantially uniform displacementfor energizationsytending to displace the armature. beyond'said uniform displacement limit, said means being assooiated with the field magnet in such a manner as to be independent of the'steady flux4 produced thereby. A

g electromagnetic :device comprising a 'ria field magnet, an armature between the poles of said magnet, a Winding for producing a variable magnetic ux through said armature and poles, and means comprising permalloy sections in the pole ieces of said magnet forlimiting the Variable flux to a predetermined amount substantially irrespective of the changes in the amplitude of the energizing force in said Winding tending to produce magnetic flux above said amount.

In Witness whereof, I hereunto subscribe my name this 29th day of October A. D. 1926.

EDWARD L. NORTON. 

